In the event of fire, smoke and heat initially rise to fill the uppermost atmosphere near the ceiling of a room or hallway. The atmosphere nearer the floor fills with smoke more slowly and affords evacuees breathable air for a longer period of time. Accordingly, when evacuating a burning building, persons are advised to do so by crawling. Conventional exit signs are normally located near the ceiling above emergency exits. So situated, the visibility of these signs is prone to being obscured by smoke, making exits difficult for evacuees to find.
Previous attempts to devise better evacuation exit indicators have typically relied upon high intensity light sources to enhance the visibility of evacuation exit identifiers. U.S. Pat. No. 4,074,225 disclosed an evacuation exit indicator device conventionally mounted near the ceiling above an emergency exit and incorporating a spot lamp emitting yellow colored light flashes which is described as being, even under some smoke conditions, at least partially visible to the floor occupants. U.S. Pat. No. 4,283,657 discloses a similar device incorporating continuously recharged auxiliary batteries to guarantee operation in the event of electrical power failure. U.S. Pat. No. 4,422,069 discloses flashable lights situated adjacent an exit door and near the floor. The flashable light sources are powered by auxiliary rechargeable batteries in the event of an electrical system failure.
Devices mounted near the ceiling may be rendered invisible by thick acrid smoke from burning plastic and other synthetic building materials. Electrical high intensity light sources may be rendered inoperable by water sprayed from overhead water sprinkler systems. Floor level flashable lights are subject to damage from normal traffic, delivery dollies and routine building maintenance such as vacuuming. Prior art devices are also costly to manufacture and install.
The object of the present invention is to provide a reliable evacuation exit indicator device which remains visible to evacuees in the event of a fire.